The invention relates generally to a device for applying tensile forces to a flexible cord and, more particularly, to a device for operating a set of traverse drapes or other window covering structure having a pull cord.
A number of hand crank mechanisms have been proposed to open and close curtains, shutters and similar structures. Examples of such mechanisms are disclosed in the following patents: U.S. Pat. No. 929,742 to Wilson; U.S. Pat. No. 1,255,817 to Gibson et al.; U.S. Pat. No. 1,726,854 to Mumford; U.S. Pat. No. 1,734,800 to Faulds; U.S. Pat. No. 1,849,371 to Gronbech.
The Faulds and Gronbech patents relate to drive wheel arrangements for frictionally engaging an actuating cord to operate a reciprocating window-related structure. However, it is difficult in devices of this type to attain sufficient friction between the cord and the drive wheel to prevent slippage. The problem of slippage is particularly acute in the operation of inexpensive traverse drapes and other window covering structures because they often present substantial drag forces which must be overcome by the device. For example, some traverse drape assemblies have been found to require forces up to approximately 40 pounds to operate.
A somewhat different apparatus is described in U.S. Pat. No. 2,341,123 to Schweller, wherein a flexible sheet metal closure is moved up and down the front of a refrigerator by a drive pulley acting through a cord. A pair of spring loaded idler rollers are provided to tension the cord, presumably increasing friction. However, the tensioning effect is a function of the spring force and is independent of the force applied to the drive pulley.
Therefore, it is desirable in many applications to provide a simple and smooth-acting device capable of applying substantial tensile forces to a flexible cord to draw the cord toward the device.